The invention relates generally to a method and an apparatus for feeding bulk material into a pneumatic conveyor conduit through which the material is then to be transported.
One form of apparatus for feeding bulk material in particulate or granular form into a pneumatic conveyor conduit, as disclosed in German laid-open application (DE-OS) No. 31 44 592, comprises a charging valve lock chamber through which the bulk material is passed from a storage or accumulation space, for example a conduit of a storage container, into the pneumatic conveyor conduit. The charging chamber can be alternately closed off relative to the storage or accumulation chamber on the one hand by means of a movable closure cone member co-operating with a seat in the form of a sealing edge disposed in opposite relationship thereto, and on the other hand, relative to the conveyor conduit, for example by means of a flap. That apparatus makes it possible to produce an almost continuous delivery flow if a plurality of such apparatuses are successively brought into operation alternately for the conveying operation. A system of that nature is known from what is referred to as tandem installations but it suffers from the disadvantage that it requires a considerable amount of expenditure in terms of operating equipment. As indicated above, the closure member is in the form of a cone member which can be actuated by pneumatic means but it is necessary to associate therewith an upstream-disposed cone-type closure member for controlling the feed flow into a metering chamber for feeding the bulk material through the apparatus, and that in turn involves corresponding apparatus expenditure. In addition however, not only does that apparatus require the upstream closure member but it also has a separate air vent valve, the vent air from which has to be suitably carried away. Furthermore, the air for closing the closure member and for producing the conveying action is introduced through a suitable feed system. The conveying air pressure must correspond to the necessary closing pressure of the closure arrangement, which in this case makes it impossible to arrive at a proper setting in respect of the operational air parameters of the equipment.
In another form of apparatus for feeding bulk material to a pneumatic conveyor conduit, as disclosed in Swiss patent specification No. 340 765, using a sealing edge providing a seat for a closure member for closing off the flow of bulk material through the apparatus, for it to pass into the conveyor conduit, operatively associated with the sealing edge is at least one annular feed passage which feeds air to a series of holes directed on to the head portion of the closure member to provide a curtain or veil of air which sweeps thereover for cleaning purposes. After the closure procedure, that air flows away unused above the closure member and cannot be used in that arrangement as useful conveying air. The supply is arranged at the position of the movable closure member and must therefore also be movable. That arrangement does not make any provision for fluid-tight connection to a storage container or the like.
In another form of apparatus for almost continuous conveying of bulk materials, as disclosed in German laid-open application (DE-OS) No. 34 20 616, the apparatus has only one conveyor container and does not involve any upstream-disposed metering arrangement. The apparatus is suitable for conveyor pressures of around 6 bars and provides for optimum use of the energy which is supplied for pneumatic conveying of the bulk material, while ensuring a substantial degree of operational reliability in all operating conditions and also operating in a substantially wear-free manner. In that arrangement, associated with each sealing edge which forms a seat for a closure cone member is at least one annular air supply passage for producing a flow of air which is directed towards the closure cone member, while a closure flap which is pivotally mounted at one end thereof is urged upwardly by a force storage means, the flap in the closure position thereof bearing against the substantially horizontal edge of a mouth opening of the charging chamber of the apparatus. The sealing edge is provided on a resilient sealing ring and is disposed above a bellows cylinder on which the closure cone member is carried and by which it is moved.